Dread-filled worry generated by helmer Jeremy Herrin’s spellbinding cast creates almost palpable static in the mysterious first act of Joe Penhall’s “Haunted Child,” when formerly missing Douglas (Ben Daniels) returns home unexpectedly a severely changed man. Sadly, it’s the other sense of “static” that dominates the disappointing second act in which Douglas tries to persuade his wife and young son of the virtues of his new beliefs, which challenge everything about their lives.

The opening scenario of a little boy (Jack Boulter at the performance reviewed) telling his mother Julie (Sophie Okenedo) in plaintive tones that he thinks he has seen and heard a ghost in their otherwise empty house is upsetting. Julie is placating but beneath her soothing tones it is horribly evident that something at home has gone seriously awry. The mood, perfectly caught, points to Penhall’s typically effective economy of means.

Then, just as audiences are puzzling out what might be happening, Penhall springs a surprise with a sudden reveal of Douglas, bare-footed, scrawny and strung-out. His startling reappearance at this early stage piles on the questions for both his family and the audience.

Penhall maintains tension by very gradually feeding facts into the situation. Increasingly exasperated Julie forces unwilling Douglas to reveal the idealism underpinning the “Group” he has joined in his surprising spiritual quest. Is it a collective of people dedicated to abnegating the modern, materialistic self, or a bunch of deluded or downright dangerous obsessives?

Problematically, Penhall chooses to stack his argument in one direction only. The potential validity of Douglas’s spiritual questioning is sabotaged by the decision to have Douglas, its new disciple, paint the group as extreme charlatans. What’s still more fatal in dramatic terms is that the group only exists via ceaselessly expository description (in Douglas’ fevered account) as opposed to being part of developing stage action. Daniels’ mesmerizing, frightening performance of a man fighting against physical and mental breakdown wins enormous sympathy, but his plight does not.

Part of that also has to do with Penhall’s refusal to allow audiences to see why and how Douglas came to be in this position. You don’t have to subscribe to a need for sentimental, over-written backstory to see that a dilemma with huge thematic weight attached to it needs to come from somewhere recognizable.

Herrin is, however, alert to Penhall’s strengths. He directs as if with a magnifying glass to seek out the minute calibrations of emotion beneath the surface of the dialogue. And while keeping a lid on any kind of overstatement from his cast, he ensures that the breadth of emotion in the writing — which includes surprising humor — is honored by the actors.

The title suggests the play’s focus is on the effects on the child of the parental war. Disturbing though Douglas’ well-intentioned behavior undoubtedly is, that emphasis on the boy is actually off-center in terms of the play’s construction. It’s a further indication that Penhall’s writing is disappointingly undermined by underplotting. The result is frustrating, because the acting throughout is so fine.

Haunted Child

Royal Court Theater, London; 386 seats; £28 $44 top

Production

A Royal Court Theater presentation of a play in two acts by Joe Penhall. Directed by Jeremy Herrin.